Mold die metal and method of making dies therefrom



Patented June 8, 1943 MOLD DIE METAL AND METHOD OF MAK- ING DIES THEREFROM Nathan H. Schermer, Detroit, Micln, assignor of one-fourth to William Isler, Cleveland, Ohio No Drawing. Application April 10, 1941, Serial No. 387,873

13 Claims.

This invention relates, as indicated, to a mold die metal and method of making dies therefrom.

In the method of making mold dies, commonly known as hubbing or hub-sinking, it has heretofore been customary to use fo the material into which the hobb is to be sunk, a metal havin low resistance to the hobb, which flows uniformly, which extrudes positively into cavities, and which generally reproduces the fine lines of the hobb.

Metals having these characteristics are difficult to find, and only one, namely Swedish iron, has been generally used, since this is the only metal which has the high ductility and low carbon content necessary for the purpose.

The disadvantages of using Swedish iron for this purpose are (1) it is relatively difficult to obtain in large quantities and is relatively expensive, and (2) it must be heat treated to produce a carburized area at the mold surface, followed by a draw to produce the desired toughness, which treatments require considerable time and involve the use of a great deal of equipment.

A primary object of the present invention is to provide a metal which has all of the aforesaid characteristics, yet is relatively inexpensive. as compared with Swedish iron, anddoes not require a carburizing treatment or draw to produce the necessary hardness and toughness of the mold surface.

I have discovered that the metals described in my United States Patents Nos. 2,087,765 and 2,087,767, as well as those described in Bonte patent No. 2,087,764 and Forbes et a1. Patents Nos. 2,087,766 and 2,087,768 are admirably adapted for use as a hobbing metal. In general, however, I have found that metals of this type described in these patents, but containing in excess of 2% carbon, are better adapted for this purpose than those containing less than 2% carbon. The

analysis of such metals may be as follows:

' 7 Per cent Carbon 1.00 to-4 Silicon .45 to 1.75 Manganese Below 1.00 Sulphur Not over .05 Iron Balance I have found, however, that a preferred analysis for hobbing metal purposes is as follows:

Per cent Carbon 2.25 to 2.50 Silicon .80 to 1.00 Manganese .20 to .25 Sulphur .015 to .02 Phosphorus .015 to .02 Vanadium .025 to .05 Iron Balance I melt the aforesaid metal and then pour it into ingots. It is desirable to retain the carbon in the combined form during solidification of the metal,

cold state.

and to this end, I have found that vanadium in the amounts set forth above helps to retard primary graphitization, of the metal, but does not obstruct graphitization of the metal during the between about 1800 F. and about 1900 F. Due

to the rather low melting point of this metal,

forging at temperatures above this range may cause some difficulties, and is therefore to be avoided. Moreover, I have found. it desirable to give the metal a few preliminary passes or light blows to break up the dendritic or cast structure. after which the metal is again placed in the furnace to be reheated. After-this preliminary 7 treatment of the metal, further rolling or forging progresses quite readily. I then anneal or graphitize the metal, and have found that the most advantageous procedure for this purpose consists in heating the metal to about 1700 F. for about three hours, cooling the metal to about 1560 F. in about minutes, cooling to about 1325 F. at the rate of 16 degrees per hour, and then cooling to 1200 F. at the rate of 10 degrees per hour. After'the temperature of the metal has dropped below 1200 F., the metal 2 may be cooled to room temperature as rapidly as desired, within practical limits.

After the metal has been thus annealed or graphitized, its characteristic microst ructure consists of a matrix of relatively pure ferrite, containing graphitic or temper carbon and less than 005% combined carbon. The graphitic or temper carbon has been precipitated uniformly throughout the mass. The Brinellhardness of the metal is about 92-96. This graphitized material is well adapted as a hobbing metal, since it is quite ductile and readily lends itself to plastic deformation in the The hobbing operation, as is well known, consists in sinking a hobb into a piece of hobbing metal, the hobb being a male die member, in order to form a die cavity or female die mold for the molding of plastics and the like, the hobbing metal being in the cold state during the hobbing operation. The hobbing metal which is the subject of the pfesent invention has low resistance to the hobb, flows uniformly, extrudes positively into cavities, and generally reproduces the fine lines of the hobb.

The graphitic carbon within the'metal apparently. acts as a lubricant to allow intergranular slipping. In using my preferred analysis as a starting point in the aforesaid method of making hobbing iron, more than 2% carbon becomes available in the 'hobbing iron as temper or graphitic carbon.

As the mold or die has been completed, it can the carbon in the iron, and then quenched directly, resulting in a hardening of the mold or die. The amount of carbon redissolved in the iron willfof counse ldepend upon the temperature to which the ironds heated before bein quenched. Tbelieve that at--1 500 F., about 70 this will produce a moldhaving q e a hard or 80 points ofcarbon are redisswut even surface,

.be heated to about 1500? F., to thereby redissolve It is thus seen that Ihave provided a bobbins forming a ferrous metal containing about 1% to about 4% carbon, about .45% to about. 1.75% silicon, and less than 1% manganese into a form suitable for hobbing, graphitizing the metal and then sinking a hobb in said metal.

2. The method which comprises plasticaily deforming a ferrous metal containing about 1% to about 4% carbon, about 35% to about 1.75% silicon, and less than 1% manganese into a form suitable for bobbins. graphitizing the metal, sinking a hobb into said metal, and then heattreating the metal to redissolve the carbon therein. 1

3. The method which comprises plastically deforming a ferrous metal containing about 2.25% to about 2.50% carbon, about .80%- to about 1.00% silicon, and from about .025% to about .05% vanadium into a form suitable for bobbing. graphitizing the metal, sinking a hobb into said metal, and then heat treating the metal to redissolve carbon and harden. Y

. 4. The method which comprises plastically deforming a ferrous metal containing about 1% to about 4% carbon, about .45% to about 1.75% silicon, and less than 1% manganese into a form suitable for hobbing, annealing or graphitizing the metal to impart thereto a structure consisting almost entirelyof a ferritic matrix having,

graphite or temper carbon uniformly distributed therein, sinking a hobb into said metal while in a cold state, and then reheating the metal at a temperature sufficient to cause carbon to become redissolved and the metal thereby rehardened.

5. The method which comprises plastically deforming. a ferrous metal containing about 1% to about 4% carbon, about .45% to about 1.75% silicon, and less than 1% manganese into a form suitable to be hobbed, annealing the metal at a graphitizing temperature to impart thereto a structure consisting essentially of a ferritic matrix having graphite or temper carbon uniformly distributed therethrough, sinking a hobb into the graphitized metal while cold, heating the metal to about 1500 F. and quenching the metal.

6. The method which comprises plastically deforming a ferrous metal containing about 2.25%

to about 2.50% carbon, about .80% to about 1.00% silicon, and about .025% to about .05% vanadium into a form suitable to be hobbed, an-

nealing the metal at about 1700 F. for'about three hours, cooling the metal to about 1560 F. in about one hour, cooling to about 1325 F. at the rate of about 16 degreesper hour, then cooling to about 1200 F. at the rate of about IO-degrees an hour, cooling to room temperature, sinking a hob into the .graphitized metal thus formed,

and thereafter hardening the metal.

' 7. The method which comprises plastically deforming a ferrous metal containing about 2.25% to about 2.50% carbon, about .80% to about 1.00% silicon, and about .025% to about .05% vanadium at a temperature between about 1800 F.. and about 1900 F. into a form suitable to be hobbed, annealing the metal at about 1700 F.

. for about three hours, cooling the metal .to about 1560 F. in about one hour, cooling to about 1325 F. at the rate of about 16 degrees per hour,- then oooling to about 1200 F. at the rate of about 10 degrees an hour, thereafter cooling to room temperature, sinkinga die member intorthe .graphitized metal thus formed to form a'mold fromsaid metal, and thereafter heat treating said mold to redissolve the carbon and harden the mold.

s. A mold formed by plastically semi-min: in.

' the cold state a graphitized metal containing 1% to 4% carbon, .45 to 1.75% silicon,,less than 1% manganese, and the balance substantially iron, and subsequently hardening the same.

9. A mold formed by plastically deforming. in the cold state a graphitized ferrous metal containing about 225% to about 2.50% carbon, about .80% to about 1.00% silicon and about .025% to ing the same.

10. A mold formed by sinking a hob into a graphitized metal in the cold state containing, 1% to 4% carbon. .45% to 1.75% silicon, less than 1% manganese, and the balance substantially iron, and subsequently hardening the same.

11. A mold formed by sinking a hobv into a graphitized ferrous metal in the cold state containing about 2.25% to about 2.50% carbon, about .80% to about 1.00% silicon, and about .025% to about .05% vanadium, and subsequently hardening the same.

12. The method which comprises providingih f a form or shape suitable for sinking a hob there-- into a ferrous metal containing about 1% to about 4% carbon,'about .45% to about 1.75%

silicon, and less than 1% manganese, graphitizing the metal, sinking a'hob in said metal, and then heat treating the metal to redissolve the carbon therein.

1a. The method which comprises providing in a form or shape suitable for sinking a hob thereinto a ferrous metal containing about 1% to about 4% carbon, about .45% to about 1.75% silicon, and less than 1% manganese, graphitizing the metal, sinking a hob into said metal while the latter is in a cold state, and then heat treating the metal to redissolve the carbon therein. I

' NATHAN H. SCHERMER. 

